I have always been a bit of a rebel. Yes, this has all been done before, all the builds, motors, drives, ect, but I don't always like to follow the flock. I see the mower blade has been used as a weapon before. So be it. And yes, I did look at the tutorials on drill drives and Bunnings red wheels, but I still wasn't happy. I also wasn't too pleased about relying on one left handed screw to deliver that power to the wheels.

So, a bit of looking, and checking today, saw this plan come to fruition. I discovered, much to my surprise, that the thread on the drill motor shaft isn't metric, but is, in fact, 3/8 UNF. This actually opens more opportunities for me. I bought a set of connecting nuts, a little bit smaller than the 3/8 shaft, so I can drill the centre out, and retap a 3/8 UNF thread into this. This will then thread directly onto the motor shaft, after being press fitted into my wheels of choice, 6 inch white Bunnings wheels. I hope the press fit will hold against the torque, but just to make sure, I will be using the large washer idea either side of the wheel hub. I can then simply use a 3/8 UNF bolt into the connecting nut, from the outside, through a washer, to hold the wheel in place.

You might find the 6" wheels are too big for drill motors - which will increase the chance of burning out the motors, breaking the gearboxes, or loosening the wheels from the shafts.

The red wheel + drill motor combo has been found to be the most reliable cheap and simple option over the years, but if you can make a more solid hub connection it will be an advantage.

The left hand screw isn't taking the torque - it's just stopping the wheel unscrewing from the thread. It's not a foolproof system, but it does work surprisingly well._________________The Engine Whisperer
- fixer of things

Fri Dec 16, 2016 3:53 pm

miles&JulesExperienced Roboteer

Joined: 19 May 2010
Posts: 3970
Location: ipswich QLD

Yep once those drills are pushibg around 13kgs they will run down fast then if you have a weapon going to its shocking how fast batteries drain- flipper at gladstone had a 4s 2amp pack and it was struggling at the end of the fight with praying mantis😱 Think 3amp might be needed next time_________________Miles Blow - Julie Pitts
www.mulesfilm.com.auwww.wombokforest.com.au

-Pickasso- Vivid Sportsman champion 2015

Sun Dec 18, 2016 1:04 am

Bundyrumandcoke

Joined: 01 Dec 2016
Posts: 31
Location: Gladstone Qld

quote:Originally posted by miles&Jules:
Yep once those drills are pushibg around 13kgs they will run down fast then if you have a weapon going to its shocking how fast batteries drain- flipper at gladstone had a 4s 2amp pack and it was struggling at the end of the fight with praying mantis😱 Think 3amp might be needed next time

Batteries have been on my mind. I know a lot of you run RC batteries, but I have been thinking of alternatives. First I wondered about 12V gel cells, or around the 5 to 7 A/H capacity. Yuasa brand comes to mind. Sealed, usually around the $10 per A/H. But then I was wondering about some of these standby starter batteries you see on TV, the Minimax springs to mind. Theres a plethoria of different ones, of different capacities. Something around the 14000 MAH can be got for less that $100. Supposed to be able to start a diesel or V8 numerous times between charges. Are these feasible?

And I have gone and got a pair of the little red wheels from Bunnings, to see if I can make them fit into the plan I have. Still using the same connecting nut fitting, I just pushed out the crap black centre fitting.

Tue Dec 20, 2016 11:10 am

Bundyrumandcoke

Joined: 01 Dec 2016
Posts: 31
Location: Gladstone Qld

And I am still toying with the chain drive for the weapon. Both sprockets will nearly be touching, so only looking at about 3inches between motor centre line and weapon centre line.

Went up to a local bike shop yesterday. He couldn't fathom what I was trying to do. But he did produce a box of odds and sods, that included a heap of different plain sprockets, just right for fitting to some sort of adaptor to the axles. I had selected about 6, until he told me they were $15 each. Ummm, no thanks. Not just for an experiment. I will try the tip shop on the weekend.

Tue Dec 20, 2016 11:14 am

NickExperienced Roboteer

Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW

Keeping the sprockets really close is a good idea - it will definitely make the chain more reliable. Be careful with bike sprockets; they use a special sized chain that is not an industry standard. Its OK if you can get by with only bike parts but you can't mix 'n match with industrial chain or sprockets._________________Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Tue Dec 20, 2016 11:23 am

chunkulator

Joined: 27 Jul 2016
Posts: 219

I have had good luck with buying #25 (aka 04C) sprockets from EBay and AliExpress. You have to wait for weeks for them to show up but you can usually choose your tooth count and bore. You can also get cheap #25 platewheel sprockets of cheap dirt bikes and such on eBay.

Burden Surplus Center in the US is also great for cheap sprockets but you need someone in the US to forward them. If you ask them to ship to Australia it is ruinously expensive.

You could also check out 428 or 416 motorcycle chain. Also check out motion dynamics.com.au.

Tue Dec 20, 2016 11:46 am

NickExperienced Roboteer

Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW

Those US surplus sites are just crazy - I wish we had them over here. If you want to buy from the US with lower postage, try using a freight forwarding service. They are almost always cheaper and usually faster too, I use HopShopGo and even Australia Post has a service:
https://shopmate.auspost.com.au/
. The only thing to watch out for is if the shipment is over $1000 AUD - you will get hit with GST and maybe import duty too. I split large purchase up into smaller orders to avoid the GST (for now)._________________Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Tue Dec 20, 2016 11:54 am

chunkulator

Joined: 27 Jul 2016
Posts: 219

For your batteries RC LiPos are the correct answer. You can have 3 or 4 A.h for around $30 at significantly higher energy/mass than gel cells and they will supply stupid amounts of current with no voltage sag until they are completely discharged. Also I if I remember gel cells are explicitly forbidden in the rules - better check carefully before going this route.

Tue Dec 20, 2016 5:35 pm

NickExperienced Roboteer

Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW

I am not sure gel calls are banned, but nobody has used them for years, for good reason:

* The lowest power to rate ratio of all the allowed battery types.
* low current capacity
* relatively long recharge times
* voltage sag under higher current loads
* short lifespan when repeatedly fully discharged._________________Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Also with gel cells, the quoted AH is for a low current discharge. A 2 AH lipol might last longer than a 7 AH gel cell in a robot fight._________________So even the rain that falls isn't actually going to fill our dams and our river systems

Wed Dec 21, 2016 3:49 am

ValenExperienced Roboteer

Joined: 07 Jul 2004
Posts: 4433
Location: Sydney

They are pretty nasty when you put a saw through them too.
Less smoke, more acid tough call which is worse lol._________________Mechanical engineers build weapons, civil engineers build targets

Wed Dec 21, 2016 8:46 am

Bundyrumandcoke

Joined: 01 Dec 2016
Posts: 31
Location: Gladstone Qld

Yep, Ok, the gell cell battery was just a fleeting thought as I saw them in passing one day.

I have pretty much abandoned the idea of using the original chassis, except for the mounts for the weapon bearings. I will have to cut and shut them into what will be the new scratch built chassis. The bearings are a stupid outer diameter of 28mm. The nearest holesaw is 29mm, so too much freeplay. Unfortunately, I don't have access to either a lathe or milling machine, so its the basics for me.

Thu Dec 22, 2016 10:09 am

NickExperienced Roboteer

Joined: 16 Jun 2004
Posts: 11799
Location: Sydney, NSW

What do you need to make holes in for the bearings? If its plastic, maybe you can melt them in to slightly undersized holes._________________Australian 2015 Featherweight champion
UK 2016 Gladiator champion